The CHARA Array measures the sizes of stars across a large range of masses and evolutionary stages (e.g., Boyajian et al. 2012a, 2012b, 2013). The angular diameter of a star, when combined with the stellar parallax (measured through astrometric missions like Hipparcos or GAIA), provides a direct measurement of the physical radius of the star. If the bolometric flux of the star is measured from its spectral energy distribution, then an empirical measurement of the stellar effective temperature can be derived through Stefan's Law (Fbol = ¼ θ2σT4).
The fundamental parameters of a star (radius, effective temperature, luminosity) can be compared with evolutionary models to estimate the mass and age of a star (Jones et al. 2015, Ligi et al. 2016).